1. Field of the Invention
The present invention relates to a liquid crystal display device and method for fabricating the same, and more particularly, to a liquid crystal display device and method for fabricating the same adapted to eliminate light leakage failure by forming pixel electrodes to overlap with data lines and gate lines.
2. Discussion of the Related Art
In general, recent developments in the information communication field have increased demand for various types of display devices. In response to this demand, various flat panel type displays, such as liquid crystal display device (LCD), plasma display panel (PDP), electro-luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed, and parts of them are used in various equipment as a display.
In particular, LCD devices have been used as the most popular portable display devices, replacing the cathode ray tube (CRT), because of their high resolution, lightweight, thin profile, and low power consumption characteristics. In addition, LCD devices have been implemented for portable image display devices such as notebook computers. Further, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Accordingly, efforts to improve image display quality of LCD devices contrast with the benefits of their high resolution, lightweight, thin profile, and low power consumption. In order to incorporate LCD devices as a general image display, image quality such as fineness, brightness, large-sized area, for example, must be realized.
Such an LCD device includes a liquid crystal panel for image display, and a driving unit for inputting a driving signal to the liquid crystal panel. The liquid crystal panel includes first and second glass substrates attached to each other with a space between the substrates, and a liquid crystal layer injected into the space. The first glass substrate (TFT array substrate) has, on itself, a plurality of gate lines arranged in a direction and spaced by a certain distance from the neighboring gate lines, a plurality of data lines arranged in a direction perpendicular to the direction of the gate lines and spaced apart by a certain distance from the neighboring data lines, a plurality of pixel electrodes arranged in a matrix configuration on the pixel regions defined by the crossing of the gate lines and the data lines, and a plurality of thin film transistors switched by signals of the gate lines and for transferring the signals of the data lines to the respective pixel electrodes. The second glass substrate (color filter substrate) has a black matrix layer for shielding the light of portions other than the pixel regions, a color filter layer of red (R), green (G) and blue (B) for representing colors, and a common electrode for implementing images. In case of an in-plane switching liquid crystal panel that uses horizontal electric field, the common electrode is formed on the first glass substrates. The first and second glass substrates are provided with a space therebetween using a spacer and are attached to each other by a sealant having the liquid crystal injection inlet. The liquid crystal is injected between the two substrates. Liquid crystal displays are currently in use as a TV, a monitor for a PC, a monitor for an aircraft and a personal portable terminal as well as a portable computer, a calculator and a watch. The applications have become various.
A related art liquid crystal display has a backlight device, but there is a problem called light leakage in which the light of the backlight device is leaked to a place other than the panel. The light leakage is caused by a rubbing direction and voltage differences between the pixel electrodes and the gate lines and between the pixel electrodes and the data lines. In other words, the light leakage may occur around the data lines and the gate lines. The light leakage around the data lines is prevented by partially overlapping the data lines and the pixel electrodes. Such a liquid crystal display that enhances the aperture ratio by preventing light leakage from occurring around the data lines is called a high aperture ratio liquid crystal display. Portions around the gate lines of the high aperture ratio liquid crystal display are not overlapped with the pixel electrodes, so that the light leakage occurs around the gate lines.
Hereinafter, the related art liquid crystal display will be described with reference to the accompanying drawings.
FIGS. 1A and 1B illustrate rubbing directions of the TFT substrate and the color filter (C/F) substrate in the related art liquid crystal display.
As illustrated in FIG. 1A, the TFT substrate has a rubbing direction of approximately 315° and the C/F substrate facing the TFT substrate has a rubbing direction of approximately 45°, which is twisted by −90° from the rubbing direction of the TFT substrate. In this state, even when multi-domains are formed, disclination at a boundary between the domains is generated, so that the light leakage occurs. In addition, a reverse-tilt area is also formed where the tilt angle of the liquid crystal molecules is formed opposite to a desired direction.
Also, as illustrated in FIG. 1B, the TFT substrate has a rubbing direction of approximately 225° and the C/F substrate facing the TFT substrate has a rubbing direction of approximately 135°, which is twisted by 90° from the rubbing direction of the TFT substrate. In this state, even when multi-domains are formed, disclination at the boundary between the domains is generated, so that the light leakage occurs. In addition, a reverse-tilt area is formed where the tilt angle of the liquid crystal molecules is formed opposite to a desired direction.
FIG. 2 is a plan view of the TFT substrate and the C/F substrate of the liquid crystal display according to the related art. FIG. 3 is a cross sectional view of the liquid crystal display, taken along the line I-I′ of FIG. 2.
As shown in FIG. 2, the TFT substrate includes gate lines 104 and data lines 105 formed perpendicular to each other to define pixel regions, thin film transistors T at the cross points of the gate lines 104 and the data lines 105, and pixel electrodes 100 connected to thin film transistors 106 and formed on the pixel regions. Some portions 102 and 103 of the pixel electrode 100 are overlapped with the data lines 105, but the pixel electrode is not overlapped with the gate lines 104 and is spaced apart from the gate lines 104 with a predetermined spacing 101.
The thin film transistor T includes a gate electrode 104a projecting from the gate lines 104, a gate insulating film (not shown in FIG. 2) formed on an entire surface including the gate electrode, a semiconductor layer 106 formed on the gate insulating film over the gate electrode 104a, a source electrode 105a projecting from the data lines 105, and a drain electrode 105b facing the source electrode 105a. The drain electrode 105b is electrically connected to the pixel electrode 100 through a contact hole. Some portions 102 and 103 of the pixel electrode 100 that are overlapped with the data lines 105 cover the reverse-tilt areas formed by the rubbing direction and a potential difference between electrodes.
When the rubbing direction of the TFT is approximately 315° and the rubbing direction of the C/F substrate is approximately 45°, the widths 102 and 103 of the pixel electrode 100 that is overlapped with the data lines 105 are 2-4 μm and 0-2 μm, respectively. This is because the reverse-tilted area formed by the shape of the disclination shown in FIG. 1A should be covered. When the rubbing direction of the TFT is approximately 225° and the rubbing direction of the C/F substrate is approximately 135°, the widths 102 and 103 of the pixel electrode 100 overlapping the data lines 105 are 0-2 μm and 2-4 μm, respectively. The reason is that the reverse-tilt area formed by the shape of the disclinations shown in FIG. 1B should be covered.
The gate lines 104 and the pixel electrode 100 are arranged spaced apart by the spacing 101 from each other and thus are not overlapped with each other, so that the light leakage may occur. To this end, the black matrix 152 formed on the C/F substrate facing the TFT substrate is widely formed to cover the thin film transistor T and the gate lines 104 sufficiently, thereby preventing the light leakage. Thus, in order to prevent the light leakage around the gate line 104, the black matrix 152 is widely formed to overlap with a predetermined portion of the pixel electrode 100 including the gate line 104, so that the aperture ratio is decreased.
Meanwhile, referring to FIG. 3, which is a cross sectional view taken along a line I-I′ of FIG. 2, gate lines 104 are formed at a constant interval on the TFT substrate 200. On the entire surface of the TFT substrate 200 including the gate lines 104 are sequentially formed a gate insulating film 107 and a passivation film 108 (for example, SiNx). Pixel electrodes 100 are formed on the passivation film 108 between the gate lines 104 and spaced apart by a predetermined interval 204 from the gate lines 104.
Here, since the gate lines 104 are spaced by a constant interval from the pixel electrodes 100, the light leakage may occur. So, the black matrix 152 is formed on the C/F substrate of FIG. 2 so as to overlap with a portion 231 of the pixel electrodes 100 including the gate lines 104.
As a result, the entire opening area 230 is decreased and thus the aperture ratio is reduced. The above-mentioned liquid crystal display has the following problems.
First, the light leakage around the gate line is prevented by overlapping the black matrix formed on the C/F substrate, so that the aperture ratio is reduced.
Second, in order to stably prevent the light leakage from occurring around the gate lines, the black matrix is formed on the C/F substrate so as to overlap with a predetermined portion of the pixel electrodes including the gate lines, so that the production costs are increased due to waste of the black matrix.